5.2.3 The Eye

• What is the eye?

  A sense organ containing receptors sensitive to light intensity and colour.
• What is accommodation?

  The process of changing the shape of the lens to focus on near or distant objects.
• To focus on a near object:

  • The ciliary muscles contract
  • The suspensory ligaments loosen
  • The lens is then thicker and refracts light rays strongly
• To focus on a distant object:

  • The ciliary muscles relax
  • The suspensory ligaments are pulled tight
  • The lens is then pulled thin and refracts light rays only slightly
• What is myopia?

  Short sightedness.
• What is hyperopia?

  Long sightedness.
• What causes myopia and/or hyperopia?

  Rays of light not focusing on the retina.
• What is the general treatment for myopia and/or hyperopia?

  Spectacle lenses which refract the light rays so that they focus on the retina.
• What are some newer technologies developed to treat myopia and/or hyperopia?

  • Hard/soft contact lenses
  • Laser surgery - changes shape of the cornea
  • Replacement lenses
• What is the cornea?

  A transparent layer at the front of the eye which refracts light.
• What is marked ‘X’ by the diagram?

  The optic nerve.

  
• What is marked ‘X’ by the diagram?

  The retina.

  
• What is the pupil?

  The gap through which light passes to reach the lens.
• What is marked ‘X’ by the diagram?

  The lens.

  
• What are the names of the two types of receptor cells in the retina? 

  Cone cells and rod cells.
• Which light-sensitive cells in the retina enable you to see in colour?

  Cone cells.
• Which light-sensitive cells in the retina enable you to see in the dark?

  Rod cells.
• The point where light focuses on the retina is called the fovea. This region contains the highest concentration of cone cells and gives the sharpest image.
• What is the purpose of the iris reflex?

  To ensure the optimum amount of light enters the eye.
• When the pupil is very large, do we describe it as 'constricted' or 'dilated'? 

  Dilated.
• Which two muscles make up the iris?

  Circular and radial muscles.
• When the eye is exposed to bright light, will the pupil constrict or dilate?

  Constrict.
• What happens to the circular and radial muscles when the pupil constricts?

  The circular muscle contracts, but the radial muscle relaxes.
• Which two structures refract (bend) light entering the eye? 

  The cornea and the lens.
• When looking at a nearby object, the light from the object hits the eye at a wide angle. This means that the eye needs to refract the light strongly. To achieve this, what should the shape of lens be?

  Short and fat.
• What is the structure labelled X?

  Suspensory ligament.

  
• What is the structure labelled X?

  Ciliary muscle.

  
• True or false? The ciliary muscle is just like any other muscle, so it can contract or relax.

  True.
• The suspensory ligament is not a muscle, it is a ligament. Can it contract and relax?

  No.
• When looking at a nearby object, the lens must be short and wide to refract the light strongly and focus the light on the retina. How do the ciliary muscle and suspensory ligaments achieve this? 

  The suspensory ligaments slacken and the ciliary muscle contracts.
• The ciliary muscle is a circle band of muscle that encircles the suspensory ligaments and the lens. 

  Which of the images, A or B, show the ciliary muscle in its contracted state? 

  A.

  
• What does long-sighted mean?

  The eye is unable to focus on nearby objects.
• One solution to long-sightedness is to wear glasses. Which type of lens would the glasses need to contain? 

  Convex.
• One solution to short-sightedness is to wear glasses. Which type of lens would the glasses need to contain? 

  Concave.
• What does short-sighted mean?

  The eye is unable to focus on distant objects.